EPROM (Electrically Programmable Read Only Memory)
WARNING: This page does not describe the selected car, but rather 333 other vehicles, including the 2007 BMW Z4, 2007 BMW X5, 2007 BMW X3, 2007 BMW M6, and 2007 BMW M5. However, it is still accessible from the selected car via links, so may be relevant.
An EPROM is a computer memory chip that can be electrically programmed, however in order to erase data that is stored on the chip it must be removed from the device and exposed to UV lighting for a specific time period. An EPROM has what is commonly called a "window" on the top portion of the chip usually located underneath a protective label, it is this area that must be exposed to UV light of a certain intensity for a specific time period in order to erase the information stored on it.
Early engine control modules (DME 3.X) and transmission control modules were the first devices which allowed technicians to first remove the chip from the module, install a new "blank" EPROM and then program the module.